Json字符串中取出指定节点值,json数组转List,把JavaBean转换为json字符串_json.tojsonstring 指定节点名称

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;

public class JacksonUtil {

    public static ObjectMapper objectMapper;

    /**
     * Json字符串中取出指定节点值
     *
     * @param jsonStr json
     * @param key     key
     * @return
     */
    public static String getValueByKey(String jsonStr, String key) {
        if (objectMapper == null) {
            objectMapper = new ObjectMapper();
        }
        try {
            JsonNode jsonNode = objectMapper.readTree(jsonStr).get(key);
            if (jsonNode == null) {
                return null;
            }
            if (jsonNode.isTextual()) {
                return jsonNode.asText();
            } else {
                return jsonNode.toString();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * @param jsonStr   json
     * @param valueType class
     * @return T
     */
    public static <T> T readValue(String jsonStr, Class<T> valueType) {
        if (objectMapper == null) {
            objectMapper = new ObjectMapper();
        }

        try {
            return objectMapper.readValue(jsonStr, valueType);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * json数组转List
     *
     * @param jsonStr
     * @param valueTypeRef
     * @return
     */
    public static <T> T readValue(String jsonStr, TypeReference<T> valueTypeRef) {
        if (objectMapper == null) {
            objectMapper = new ObjectMapper();
        }

        try {
            return objectMapper.readValue(jsonStr, valueTypeRef);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 把JavaBean转换为json字符串
     *
     * @param object
     * @return
     */
    public static String toJSon(Object object) {
        if (objectMapper == null) {
            objectMapper = new ObjectMapper();
        }

        try {
            return objectMapper.writeValueAsString(object);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}



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